It is customary in industry to lubricate machines according to a pre-established lubricating plan. The monitoring of such lubricating plans has been carried out by means or graphs or time charts which presuppose high reliability on the part of those responsible for the monitoring.
It is furthermore known to monitor lubricating plans by means of programmed cards and computers. This monitoring, however, is expensive, especially for small organizations. Consequently, there is a demand in the industry for a fool-proof signal-generating device, in particular a warning device, which obviates the need for human monitoring and which addresses itself directly to the appropriate implementing organization, by means of appropriate signals.